In a parallel post, I just agreed with you. But jerf's position may be closer to correct than you suspect, because fuel economy is also part of the regulations. Well, you can meet both if you make the car lighter. But collision resistance is also part of the regulations. And so on...
Did the patched cars also meet mileage standards? How close to the limit were they? (Or are there no mileage standards for diesels?)
1. Again, theoretically there will be a limit where these will converge for diesel and petrol vehicles. At that point, I predict that EVs, hybrids, and fuel cell vehicles will offset the overall requirements.
2. Collision resistance has improved as weight has decreased.
3. Did they meet mileage standards? Maybe. Probably. 46mpg (the resultant fuel economy after the patch) appears to be outstanding even for diesel vehicles. Mileage is imposed on individual models by year targets and also manufacturer-wide. That is why cars in general are sold with much lower margins: to help manufacturers offset the poor fuel economy and emissions of larger vehicles.
Empirically, VW released patches for their cars to bring the non-test characteristics in line with their test-mode characteristics.
The outcome was that the diesel-engine vehicles had reduced fuel economy and acceleration. [1]
Most customers still enjoyed their cars after the patch was applied.
1. http://www.consumerreports.org/cro/cars/guide-to-the-volkswa...